1. Field of the Invention
The present invention generally relates to a shock absorber with adjustable damping force, comprising a pressure tube filled with damping medium, in which a piston on an axially movable piston rod divides a work chamber into a piston-side chamber and a non piston-side chamber, whereby there is a damping medium flow between the two work chambers, which is divided into a main flow and a bypass flow, a damping valve device consisting of a damping valve body, with a main stage valve for each flow direction, each of which is formed by a main stage valve body, and a pilot stage valve which activates the main stage valve, an adjustable actuator, which controls a flow connection between the control chamber and a work chamber.
2. Background Information
German Laid Open Patent Application No. 41 18 030 discloses a shock absorber which is equipped with a damping valve device which is formed by a main stage valve and a pilot stage valve. The pilot stage valve for each flow direction essentially consists of a dummy piston, possibly a balance piston, which can move axially inside a pilot chamber. The dummy piston is displaced by the pressure force of the damping medium, whereby the motion of the two dummy pistons under the influence of the damping medium takes place simultaneously and in the same direction of movement. In other words, during the influx, the dummy piston facing the work chamber to be reduced in size is moved into the pilot chamber, and the other dummy piston is moved out of it. Such a configuration tends to require an increased amount of axial space for the damping valve device. Overall, the size of the valve device is a significant disadvantage.
An additional disadvantage of this valve design is that leak currents from the pilot chamber have a significant effect on the opening action of the main stage valve. The diaphragm gland between the connecting pipes, or tubes, of the valve device and the two dummy pistons, as well as the leakage losses between the slide valve and the tube, tend to add up. These leakage losses are predominantly a function of the tolerances of the components in question. Consequently, the opening action of the main valve stage is indirectly a function of the leakage losses.